My arm creaks when I make a fist?

Tendinitis. "intersection syndrome" is a form of tendinitis (actually "tenosynovitis") of the wrist and thumb tendons located on the back side of the wrist just above the joint. This makes a very stereotypical "creaking" sound as you move your wrist. Arthritis can make a crunchy-like sound/sensation at a joint.
Noises. If it doesn't hurt but makes a noise it is most likely a vaccuum phenomenon in a joint. This is normal. No harm will come from cracking your joints unless you do it against a concrete wall.
Needs to be checked. I'm assuming you mean your wrist and if so this could represent an unrealized ligament injury to the wrist that creates instability of the bones causing "creaking" or possibly an undiagnosed fracture. These possibilities need to be checked out. Best of luck.
Normal. Craking of the joint most likey normal it happen when try to move your joints have not move for a while, some people make it a habit to crack there jiont, I would not recomend that. Some could a sign of arthitis of the jionts.